Switch to manual trait impls for sigevent

`sigevent` on most platforms have padding or unused fields. Rather
than display those in the `Debug` impl by deriving it, manually implement
all `extra_traits` instead ignoring those fields.

I do worry that my `PartialEq` implementations for this for some platforms (like Linux) is not correct due to ignoring bytes that shouldn't be ignored because these structs don't have a proper union set up.

cc @asomers
Part of nix-rust/nix#1035

sigevent structs on most platforms have padding or unused fields. Rather
than display those in the Debug impl by deriving it, manually implement
all extra_traits instead ignoring those fields.

Fix libstd compilation for arm-uclibc target

linux: add VSOCK struct and constants

Add struct sockaddr_vm and VMADDR_ constants to use VSOCK on Linux.
VSOCK is present since Linux 3.9

Re-add PTRACE_DETACH for mips64 GNU targets

During the refactor in 4bd419eb, `PTRACE_DETACH` was accidentally removed on
these targets. This re-adds it.

Fixes brokenness encountered during nix-rust/nix#1035

CC @asomers

During the refactor in 4bd419eb, PTRACE_DETACH was accidentally removed on
these targets. This re-adds it.

Add more posix message queue functions for Linux and all for solarish

I'm not able to run the tests locally (likely due to too old headers on Ubuntu 18.04), but I've tested my [posixmq crate](https://github.com/tormol/posixmq/tree/0decb7c82dd472024c7e90fd8121671881a81ae2) with these functions on Linux and OmniOS.

Refactor the GNU module

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Add struct sockaddr_vm and VMADDR_ constants to use
VSOCK on Linux. VSOCK is present since Linux 3.9

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Rename the notbsd module to linux_like

Upgrade rlimit consts

cc @aidanhs - this should fix the error you are seeing.

Fix type of RLIMIT consts on linux gnu

Add missing TIOCGRS485, TIOCSRS485 constants to Linux

Closes #1094 .

Deprecate fixed width integer type aliases

cc @emilio - I think it makes sense to ensure that the latest released version of bindgen works properly with this change. That is, that even when asked to use C types from, e.g., `libc::`, it does not use aliases for the fixed-width integer C types (e.g. `libc::int64_t`) but uses Rust primitive types instead (e.g. `u64`).

Closes #1304 .

Add statx on Linux

Closes #1178.